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Commit 7088efa9 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

fs/dcache: Use release-acquire for name/length update 



The code in __d_alloc() carefully orders filling in the NUL character
of the name (and the length, hash, and the name itself) with assigning
of the name itself.  However, prepend_name() does not order the accesses
to the ->name and ->len fields, other than on TSO systems.  This commit
therefore replaces prepend_name()'s READ_ONCE() of ->name with an
smp_load_acquire(), which orders against the subsequent READ_ONCE() of
->len.  Because READ_ONCE() now incorporates smp_read_barrier_depends(),
prepend_name()'s smp_read_barrier_depends() is removed.  Finally,
to save a line, the smp_wmb()/store pair in __d_alloc() is replaced
by smp_store_release().

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <linux-fsdevel@vger.kernel.org>
parent cb7e125e

fs/dcache.c

+3 −7
Original line number Original line Diff line number Diff line
@@ -1636,8 +1636,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name) 
	dname[name->len] = 0;

	dname[name->len] = 0;





	/* Make sure we always see the terminating NUL character */

	/* Make sure we always see the terminating NUL character */

	smp_wmb();

	smp_store_release(&dentry->d_name.name, dname); /* ^^^ */

	dentry->d_name.name = dname;





	dentry->d_lockref.count = 1;

	dentry->d_lockref.count = 1;

	dentry->d_flags = 0;

	dentry->d_flags = 0;
@@ -3047,17 +3046,14 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen) 
 * retry it again when a d_move() does happen. So any garbage in the buffer

 * retry it again when a d_move() does happen. So any garbage in the buffer

 * due to mismatched pointer and length will be discarded.

 * due to mismatched pointer and length will be discarded.

 *

 *

 * Data dependency barrier is needed to make sure that we see that terminating

 * Load acquire is needed to make sure that we see that terminating NUL.

 * NUL.  Alpha strikes again, film at 11...

 */

 */

static int prepend_name(char **buffer, int *buflen, const struct qstr *name)

static int prepend_name(char **buffer, int *buflen, const struct qstr *name)

{

{

	const char *dname = READ_ONCE(name->name);

	const char *dname = smp_load_acquire(&name->name); /* ^^^ */

	u32 dlen = READ_ONCE(name->len);

	u32 dlen = READ_ONCE(name->len);

	char *p;

	char *p;





	smp_read_barrier_depends();



	*buflen -= dlen + 1;

	*buflen -= dlen + 1;

	if (*buflen < 0)

	if (*buflen < 0)

		return -ENAMETOOLONG;

		return -ENAMETOOLONG;